The present invention relates to a torsional vibration damping device and a lock-up clutch in a torque converter comprising three kinds of vane wheels (impeller, turbine and stator) wherein torque is transmitted by means of hydraulic fluid. The impeller is fixed to a-front cover connected to an input rotation member, and the turbine is rotated by the hydraulic fluid flowing from the impeller.
Some torque converters include a lock-up clutch between the turbine and the front cover. The lock-up clutch transmits torque from the front cover to an output member directly. The lock-up clutch includes elastic members such as torsion springs in order to absorb torsional vibrations. It is preferable that the torsional springs have low rigidity so as to prevent noise at the idling or driving of a vehicle. Low-rigidity torsion springs are, however, a cause of large vibration of the vehicle in the front-to-rear direction when low frequency vibration is generated by acceleration or deceleration during the lock-up engagement.
In order to solve the above mentioned problem, Japanese Utility Model Laying-Open document No. 123258/1986 shows a viscous damping mechanism and an elastic connection device which function in parallel. The-torsional vibration damping device mainly comprises a first cylinder provided on the input rotation member, and a second cylinder connected to an output member, wherein an annular fluid chamber is formed between them. The first cylinder and second cylinder are provided with partition plates alternately extending toward each other, wherein a clearance is defined between the ends of the partition plates and the cylinder end surface opposite. When both cylinders are made to twist relative to each other by torsional vibration, the fluid flows through the clearance giving rise to viscous damping.
In the above described structure, accuracy of the clearances is low. That is, when both cylinders are fixed to the input member and the output member respectively, the clearances become different because of working errors and assembly errors. Moreover, when the temperature of the fluid rises due to viscous friction, the fluid viscosity becomes low such that the viscous damping decreases and desired damping effects cannot be obtained.